1. Field of the Invention
The present invention relates to an electron-emitting device and an image display apparatus using the electron-emitting devices.
2. Description of the Related Art
As an electron-emitting device, there is an electron-emitting device of a field emission type, a surface conduction type, or the like.
As a step of forming the surface conduction electron-emitting device, first, a pair of device electrodes is formed onto an insulating substrate. Subsequently, the pair of device electrodes is connected through an electroconductive film. By applying a voltage between the device electrodes, a process called “energization forming” for forming a first gap into a part of the electroconductive film is executed. The energization forming operation is a step of supplying a current to the electroconductive film and forming the first gap into a part of the electroconductive film by a Joule heat generated by the current. By the energization forming operation, a pair of electroconductive films which face through the first gap is formed. Subsequently, a process called “activation” is executed. The activation operation is a process for applying a voltage between the pair of device electrodes in an atmosphere of a carbon-containing gas. Thus, electroconductive carbon films can be formed onto the substrate in the first gap and the electroconductive films near the first gap. Thus, the electron-emitting device is formed.
When an electron is emitted from the electron-emitting device, an electric potential which is applied to one of the device electrodes is set to be higher than an electric potential which is applied to the other device electrode. By applying the voltage between the device electrodes as mentioned above, a strong electric field is caused in a second gap. It is, consequently, considered that electrons tunnel from a number of portions (a plurality of electron-emitting regions) in a portion forming an outer edge of the second gap corresponding to an edge of the carbon film connected to the device electrode on the low potential side and a part of the electrons are emitted.
As for the electron-emitting device, it is demanded to improve stable electron-emitting characteristics and an electron-emitting efficiency so that an image display apparatus using the electron-emitting devices can stably provide a bright display image. The efficiency used here is evaluated by a ratio of a current flowing between a pair of device electrodes of the surface conduction electron-emitting device (hereinbelow, referred to as a “device current”) when a voltage is applied between the device electrodes and a current which is emitted into a vacuum (hereinbelow, referred to as an “electron emission current”). Therefore, the electron-emitting device in which the device current is small and the emission current is large is demanded. If the electron-emitting characteristics and efficiency which can be stably controlled are improved, for example, in an image display apparatus using phosphor as an image forming member, a high-quality image display apparatus which is bright at a low current such as a flat panel television can be realized. In association with the realization of the low current, costs of a driving circuit and the like constructing the image display apparatus can be also reduced.
When an activation time extends, an emission current amount of the surface conduction electron-emitting device decreases contrarily. Initial emission currents of the respective electron-emitting devices are not substantially uniform and the devices show different activation characteristics due to such causes that a gas pressure during the activation differs depending on a location and the like. That is, when the activation is executed at the same time, the devices have a variation in efficiency. Therefore, in the case where the image display apparatus is constructed by using a plurality of surface conduction electron-emitting devices, there is such a problem that if the efficiencies of the electron-emitting devices are not uniform, the electron emission amount changes depending on the position of the device or a luminance fluctuation occurs.
In Japanese Patent Application Laid-Open No. H09-293448, there has been disclosed such a construction that an activation suppressing layer is formed onto an insulating substrate, an activation accelerating layer is further stacked onto the activation suppressing layer, and an electron-emitting device is formed, thereby suppressing a deterioration in characteristics due to the over-activation and uniforming the activation in an activating step.
However, in the electron-emitting device disclosed in Japanese Patent Application Laid-Open No. H09-293448, there is such a problem that a device current (leakage current) flowing in a substrate occurs due to the existence of the activation suppressing layer and the efficiency deteriorates.